About 75% of production losses in the world can be directly attributed to diseases (Agrios 1997). In this context, approximately 24% of world potato production is lost due to diseases caused by bacterias, with approximately 40% of losses sometimes occurring in developing countries (Oerke, 2006). In order to avoid losses, the use of agrochemicals is indispensable in agriculture. However, the use of these techniques for diseases control is increasingly questioned with regards to their impact on the environment and human health. So as to overcome this impasse, conventional improvements have developed cultivars that are more resistant to diseases. Nonetheless, resistant varieties to bacterial diseases are still rare (Yi et al., 2004).
Plant adaptation and resistance to diseases occur due to considerable alterations in cells metabolism, such the protein synthesis and defence molecules, induced through complex mechanisms involving the pathogens presence recognition.
The activation of latent resistance mechanisms in plants, by administering elicitor agents represents an alternative for the agricultural diseases control, without the use of substances with direct effects on phytopathogens and often toxic effects for humans, such as fungicides, bactericides and nematicides. According to Medeiros et al., (2003), contact between the pathogen and the host plant cell unleashes synthesis reactions of compounds that are toxic for the pathogen, imitating in a rudimentary human and animal immunological systems.
In some cases, it is difficult to determine if the plant response occurs before or after the pathogen recognition. However, generally when the plant is attacked by micro-organisms it is capable of producing inhibiting molecules next to the penetration location, promoting growth inhibition of the pathogens.
Natural selection and the co-evolution of plants with pathogens have caused plants to select a series of defence mechanisms. As such, it is believed that the difference between resistance and susceptibility may be the result of time variations, cellular autonomy or the intensity of plants defence responses (Moraes, 1998).
The recognition of pathogens for activating defence responses in non-host plants, is probably determined by invariable standards in molecules associated with the pathogens, which are characteristic of all classes of microorganisms, thereby inducing signalling cascades, partially similar to those that mediate the innate immune responses in animals (Nürnberger e Lipka, 2005).
The term elicitor was originally used to refer to molecules and other stimuli that induce synthesis or accumulation of anti-microbial compounds (phytoalexins) in plant cells. Phytoalexins constitute a heterogeneous group of subsequently-formed substances, which do not contain nitrogen in their molecules, among which, (cyclical or non-cyclical) isoflavonoid, furanoacetylene or terpenoid compounds seem to be the most important (Romeiro, 2001). Currently, the term elicitor is used for molecules that stimulate some kind of self-defence mechanism in plants, such as the accumulation of anti-microbial phytoalexins, the inducing of cell death (hypersensitivity reaction) and the synthesis of proteins that inhibit degrading enzymes produced by pathogens (Hahn, 1996). Generally, elicitors are molecules on the surface of a pathogenic micro-organism of a plant, which, when applied in host or non-host plants, induce resistance reactions typical of the pathogen-plant system studied (Kortekamp and Zyprian, 2003). The location of the hosts receptors, which recognise the elicitors of the pathogens, is largely unknown. Studies indicate that these receptors exist in the plasma membrane or outside of it, while other appear to be located in intracellular areas (Hutcheson, 1998).
Plants react to a pathogen infection by inducing resistance of a long duration and a wide spectrum to subsequent infections. This resistance response induced against diseases has been known for many years under different names, such as acquired physiological immunity or induced resistance; here we will refer to it using the abbreviation SAR, from English, (Systemic Acquired Resistance) (Ryals et al., 1994).
The phenomenon of inducement of systemic resistance or systemic acquired resistance was defined as being the activation of resistance against diseases, induced systematically in plants, by a localised phytopathogen infection, or in response to the administration of different abiotic agents. Among said agents, we can cite β-aminobutyric acid (BABA), salicylic acid (SA) and the respective analogous, functional agents such as 2,6-dichloroisonicotinic acid (INA) and s-methyl ester from benzo-(1,2,3)-thiadiazole-7-carbothioic acid (acibenzolar-S-methyl, ASM) (Herbers et al, 1996; Guzzo, 2004). Furthermore, SAR can be induced by different molecules, such as carbohydrates, glycoproteins, proteins and lipids (Ricci et al., Hahn et al., 1996). These molecules can originate from extracellular lipopolysaccharides in bacteria, glycoproteins from the cell wall of pathogenic fungi, carbohydrates from the cell wall of non-pathogenic fungi and so forth (Hahn and Albershein, 1978; Koch et al, 1998; Coventry and Dubery, 2001). To this end, Wulff and Pascholati (1999), carried out the partial purification and biochemical characterisation of a glycoprotein elicitor present in the cell wall of Saccharomyces cereviseae, capable of inducing the synthesis of phytoalexins in weakened mesocotyls of sorghum.
In Solanum tuberosum, SAR can be induced by the components of the cell wall of hyphae of the fungus, Phytophthora infestans, such as Pep-13 oligopeptide (Halim, 2004), in which local and systemic oxidative burning occurs. As such, local treatment with the elicitor on the leaflets of compound leaves of a plant, induced sub-systemic, local oxidative burning, that is, in other untreated leaflets of the same leaves, besides systemic burning (Park et al., 1998; Vleeshouwers et al., 2000). In tissues that are distant from the inoculation site in Arabidopsis leaves with the avirulent pathogen, Pseudomonas syringae, SAR progressed more effectively in younger leaves and this response was associated with a large accumulation of salicylic acid (Zeier, 2005).
Various agents can induce defence metabolism in plants, fostering lasting protective reactions against a broad range of phytopathogens. These agents (products) represent a new generation of commercial agricultural defences that in general do not produce a direct effect on pathogens, but bring about a increase in plant resistance.
Since the discovery of the plant resistance inducer, s-methyl ester from benzo-(1,2,3)-thiadiazole-7-carbothioic acid (known as Acibenzolar-S-Methyl®, or ASM), a great advance has occurred in the development of products which take advantage of the activation capability of different defence mechanisms in plants. The commercial product, Acibenzolar-S-Methyl (ASM), whose commercial name is Actigard® (Europe) or Bion® (Brazil), produced by the company Novartis, was registered in Brazil for the cultivation of tomato, citruses and cocoa. ASM seems to operate by inducing the synthesis of a phytoalexin molecule (coumarin) and a rapid accumulation of phenolic compounds in barley plants, reducing the penetration of fungi in the leaves. Accordingly, the administering of ASM in wheat induces the synthesis of resistance proteins (PR proteins) in the plant.
Messenger®, produced by the company Eden Bioscience, is a commercial product whose active ingredient is a protein known as harpin, which was isolated and purified using the bacteria, Erwinia amylovora, and produced artificially, for commercial purposes, as Escherichia coli. This protein weighs 44 kDa and is highly stable at high temperatures, naturally being associated with the bacteria wall. After spraying the Messenger®, the harpin protein attaches to the receptor of the plant cell and unleashes defence responses approximately 5 to 10 minutes after its application, with the defence response being completed after three to five days (Eden Bioscience, 2002). The product is not toxic to animals and quickly deteriorates under the effect of solar radiation or through the action of decomposing organisms both on the surface of the plant and in soil.
Milsana®, produced by KHH BioSci Inc, made from leaf extract from the plant, Reynoutria sachalinensis (giant knotweed—Polygonaceae). The dry and ground plant material (5 g) is mixed with ethanol (100 ml) and sprayed on the plants. It was registered as a bio-pesticide in the USA in 2000 and is used with ornamental plants (greenhouse), helping in protecting against Oidio spp. and the grey mould, Botrytis cinerea. This plant extract induces the accumulation of PR proteins and phytoalexins, causing an increase in plant defence.
Cucumber plants (Cucumis sativus) treated with Milsana® increase their resistance against Sphareotheca fuliginea, fostering an increase in the plant of endogenous defence mechanisms such as an elevation in the activity of peroxidases, β-1,3-glucanases, as well as the production of glycosylated phenolic compounds, which are toxic for micro-organisms (Daayf et al., 1995). This compound has variable and dependent effects from the cultivar being protected. However, this compound is not toxic for animals and can foster protection results similar to those obtained when using conventional fungicide.
Oxycom®, produced by the company Redox Chemicals, is a combination of an inducer (peracetic acid) from the production of oxygen reactive species (Hammerschimidt et al., 2001) and a mix of nutrients. In species of bean plants, this product induces the expression of genes related to defence, codifying proteins involved in the metabolism of phenols and the thickening (reinforcement) of the cell wall, as well as that of peroxidases and protein extensines in tobacco (Anderson et al., 2001).
Neemazal®, produced by the company EID-Parry, is a product obtained from extracts of the plant Neem (Azadirachta indica), which has been marketed as insecticide. The active ingredient of the extract is a triterpene with a 5% concentration in the commercial product.
Ecolife 40®, produced by the company Quinabra, is made up of citrus bioflavonoids (vitamin P), ascorbic acid (vitamin C), lactic acid and citric acid, industrially obtained through the fermentation and/or extraction of organic substrates taken from citric plants, as well as polyphenols and phytoalexins. The product has various mechanisms of action, of which resistance inducement via the increase of phytoalexin synthesis seems to be one of the most important (Motoyama, 2001). The product is efficient in some pathosystems. Jayme et al. (1999) and Castro et al. (1999) highlight the efficiency of the product with regards the control of powdery mildew and rust in the bean plant. Similarly, Gasparotto et al. (2000), demonstrated that this product was efficient in the control of the disease black Sigatoka (Mycosphaerella fijiensis), displaying protection levels similar to those obtained with tebuconazole fungicide, with the advantage of not leaving residues on the fruits (Sanhueza, 2002).
Elexa® has as its active ingredient a carbohydrate molecule derived from chitin. In the USA, there are three products which contain chitin: Elexa® (0.95% chitosan); Hygra Yield Enhancing Seed Treating Agent (2.5% chitosan) and Yea Poly-D-Glucosamine Solution (2.5% chitosan). Chitosan is a polysaccharide which occurs mainly in animals from the Arthropoda phylum and its mechanism of action in plants is similar to that observed when a fungus attacks a plant. The pathogen is perceived by the recognition of chitin monomers, causing biochemical reactions that culminate in the expression of the Systemic Acquired Resistance (SAR). This product is sprayed on strawberry, tomato and apple crops, bringing about an increase in the plants' resistance.
Oryzemate®, produced by BioSafe, is used principally in rice farming as a fungicide agent. However, it was demonstrated that this product does not have a direct effect on rice pathogens, but it encourages an increase in the plant's resistance against micro-organisms. This product's ingredients include 2-sulphamoilbenzoato, saccharin and N-β-D-glucopyranosylsaccharin. This mix of molecules induces the expression of the defence protein PRR1, encouraging resistance against the pathogen, Pyricularia oryzae. 
Extracts from bacterial cultivation can be used as biopesticides. According to the definition adopted by the United States Environmental Protection Agency (EPA), biopesticides are certain types of pesticides derived from natural materials such as animals, bacteria and certain minerals (www.epa.gov/pesticides/biopesticides). Although the EPA currently displays a numerous list of registered products such as biopesticides, including those which induce systemic resistance in plants, many other products that encourage plant resistance are not registered as biopesticides due to the high costs in registering a product such as pesticide (Anderson et al., 2006).
Printed sources on patents contain various documents related to elicitor compositions, of which the most relevant for the invention herein are described below.
The document, PI 0402152-5, consists of a biological control on yeast and fungi in stocked food or in the field by way of a process of predation carried out by yeast of the genus, Saccharomycopsis. The document, PI 0402152-5, uses exotic live yeast originating from Canada, which are introduced directly over plants, or part of them, that must be preserved from the action of degrading micro-organisms or toxin producers.
The document, U.S. Pat. No. 5,968,504, uses the fungus Gliocladium catenulatum as a biological control agent through the competition and inhibition mechanism against the growth of pathogenic fungi.
The invention herein differs from the cited documents as it encourages an increase in plants' defence metabolism, without interacting directly with degrading microorganisms and microorganisms which cause diseases in plants. As such, the invention herein does not depend on the existence of the antagonistic ecological interaction, such as competition, parasitism, the production of antibiotics, and it does not entail the risk of the opportunist colonisation of animals and humans.
The document, PI 0418380-0A, consists of the use of a compound mixture of biological extracts, which when sprayed on plants encourage the inducement of resistance in plants against attacks from phytopathogenic Xanthomonas. The product consists of a mixture of extracts of non-phytopathogenic Xanthomonas spp., Trichoderma harzianum and the plant, Yucca schidigera. The product encourages inducement of the natural defence system of plants against the variety, Xanthomonas spp., and its variations.
The invention herein differs from the said document as it encourages resistance against a pathogen unrelated to the bacteria from which the extract originated. The invention herein consists of an extract containing Xanthomonas axonopodis pathovar citri, which, preferably sprayed on plants, plantlets and seeds, such as Solanum tuberosum, induces natural plant defences against bacteria and pathogenic fungi, preferably the bacteria, Erwinia carotovora, and the fungus, Alternaria solani, in plants of the Solanaceae family. The document, U.S. Pat. No. 6,242,420, refers to the use of a protein (molecular weight of 18 kDa) extracted and purified from cultures of the fungus, Trichoderma virens, and applied in the form of a solution on plants, plantlets and seeds.
The present invention differs from this document, as it uses an extract of Xanthomonas axonopodis pathovar citri containing both structures derived from the cell wall and cytoplasmic components.
Therefore, one can see that prior art does not describe or even suggest the objects of the invention herein, and as a result it meets patentability requirements.